Entamoeba histolytica is an invasive intestinal pathogen which causes substantial worldwide morbidity and mortality. Interference with intestinal colonization or mucosal invasion by amebae would prevent disease. The overall objective of this proposal is to define the basic mechanisms by which amebae adhere to and destroy host tissue; the results of which should have application in the control of clinical amebiasis. Using their different temperature sensitivities, we have been able to separate two independent steps in ameba:target cell interactions: First, a specific adherence step that is inhibitable by n-acetyl-D-galactosamine (GALNAc) and second, the rapid killing of target cells by adherent amebae. The specific aims and methods of this proposal are: 1) To isolate the amebic protein(s) that are responsible for adherence and killing of target cells by amebae. Amebic proteins responsible for adherence will be isolated by GALNAc affinity chromatography and characterized by sodium dodecyl sulfate gell electrophoresis. Amebic proteins and antibody produced against them will be assayed using established in vitro systems, for their ability to inhibit amebic adherence and for their ability to block or induce cytolysis of target cells. 2) To characterize the mechanism of the ameba cytolethal event which follows adherence to target cells. The role of ion fluxes will be evaluated by pharmacologic manipulation of amebic killing, direct measurement of target cell membrane electrical changes using microelectrode techniques, and evaluation of the effects of amebic proteins or products on rat intestinal mucosa in the Ussing chamber. 3) To establish an animal model of intestinal disease that parallels that in humans. Pathogen free Wistar strian suckling rats will be inoculated intraesophogeally or rectally with amebic trophozoites and observed for pathologic changes, for cyst excretion and for enteric or other disease. The efficacy of immunization with antibody to specific amebic proteins in prevention of colonization or alteration of infection will be investigated. Long term goals of this work include development of an effective human vaccine, use of specific antibodies to examine amebic strain variation, examination of host defenses, and pharmacologic manipulation of E. histolytica to alter its cytolytic capacity and thus prevent or arrest the invasive disease.